1. Field of the Invention
The present invention relates to an end face, pusher-type mechanical seal construction and, more particularly, to a mechanical seal construction having an improved structure for effecting and maintaining positioning or locking of the stationary seal element in the construction.
2. Description of the Background
Numerous different mechanical seals have been proposed to effect sealing around a shaft to prevent leakage of both sealing fluid and operating fluid from an enclosure. Typical of such mechanical seal assemblies are shown in U.S. Pat. Nos. 3,836,157 and 2,685,464.
The above-mentioned patents describe various means of keying the rotating shaft and the rotating seal element together (U.S. Pat. No. 3,836,157) or keying the stationary seal element to the seal gland or other fixed structure in which the seal assembly is mounted (U.S. Pat. No. 2,685,464).
There are several inherent problems associated with mechanical seal assemblies. For one, most are relatively complicated in design having a large number of parts resulting in a size which generally precludes their installation in confined spaces. For example, in pusher-type mechanical seals, springs are used as energizers, generally to urge the stationary seal element into sealing engagement with the rotating seal element. These springs are in the form of compression coil springs, as shown in the aforementioned patents. When coil springs are employed as energizers, there may be a single coil spring which is disposed in generally surrounding relationship to the shaft which is being sealed, such as shown in U.S. Pat. No. 2,685,464. Alternatively, a plurality of spaced coil springs can be disposed at circumferentially spaced locations around the shaft. Whatever the arrangement, the use of coil springs poses problems in obtaining uniform loading. Wave and Belleville springs have also been used in mechanical seal assemblies.
It is common, as shown in U.S. Pat. No. 2,685,464, to key or position the stationary seal element to the gland or other fixed seal structure by means of balls which are disposed in registering grooves in the carrier for the stationary seal and in the gland or other fixed portion of the seal assembly. As shown in U.S. Pat. No. 2,685,464, three of such key or locking assemblies can be employed at generally equally spaced circumferential positions around the shaft to maintain concentricity. The balls in engagement with the registering grooves permit relative axial movement of the stationary seal with respect to the gland or other fixed seal element and thereby allow the spring to maintain a pressure against the stationary seal urging it into sealing engagement with the rotating seal element. However, the use of elongate grooves forming an elongate keyway in which the balls ride permits the balls to move to different relative axial locations possibly causing the loss of concentricity within the seal structure and binding between the seal elements.
U.S. Pat. No. 3,836,157 discloses keying the rotating seal element to the rotating shaft by means of a key assembly comprising a hemispherical recess in which is received a ball having a radius substantially the same as that of the recess, the ball also being received in an elongate groove in a collar disposed in surrounding relationship to the shaft and rotatable therewith. In the assembly shown in U.S. Pat. No. 3,836,157, a single ball is employed, the ball being used primarily as a drive connection between the shaft sleeve and the collar to impart rotatable motion to the rotating seal elements.